Abstract
The aim of this study was to compare the humeral retrotorsion angle (HRA) of baseball players with an internal impingement with HRA of asymptomatic baseball players. CT scans were made for 18 shoulders of 9 baseball players with an internal impingement, with an average age 22.9 years old. The mean baseball career was 15.7years. We selected 33 asymptomatic baseball players as a control group. On each scan, the angle between the perpendicular line to the line connecting the peripheral margins of the articular surface of the humeral head and the line connecting the central point of the humeral epicondyle was taken as HRA. Paired and unpaired ttests were used to analyze these results. The mean HRA was 50.73°on the throwing side and 38.00°on the non-throwing one in internal impingement. In the control group, the mean HRA was 40.68°on the throwing side and 32.8°on the other one. HRA of the throwing side was signtficantly larger than that of the nonthrowing side respectively. However, there was no statistical difference in HRA of the throwing side between the internal impingement and the control group. In 1992, Walch et al. measured retroversion of the humerus in 16 overhead throwing athletes with internal impingement. They reported that retroversion on the throwing side was smaller compared with the non-throwing side, and suggested that the deficit of retroversion was one of the causes of the internal impingement, In our series, the average of retroversion of the humerus was 50.73°, and this was similar to the results that we previously reported on retroversion of 32 baseball players without internal impingement. Our results suggested that the deficit of retroversion was not a cause of internal impingement. Our study demonstrated that HRA of the throwing side was larger than that of the non-throwing side, and was unrelated to the symptoms with internal impingement.
